For the production of particleboard, chipboard and structural members of various shapes, it is known inter alia to extrude a hardenable composition consisting of the vegetable-matter (usually wood) particles with a hardenable binder (usually a thermosetting resin with water-resistant properties such as a phenol-formaldehyde, melamine, resorcinol resin) using an extrusion press. In the extruder channel, heaters may cause setting or hardening of the extruded composition which, upon emergence from the extruder, can be cut to desired lengths.
The particular type of extrusion process which is involved in this invention originates from the work described in the German patent document-printed application DE-AS No. 12 47 002, in which efforts were made to align the bits or particles included in the extrudate in a particular direction by the extrusion process.
For this purpose a mixture was first precompressed in a first compression process by a vertically operating precompression piston with considerable compression force in a compression channel and then compressed in a second compression process by a horizontally operating extruder piston.
When one practices these teachings, one can determine that the bits assume an orientation which is parallel to the upper surface near the upper surface, as has been long known from the nature of the pressing process by the extruder press plate.
However in the core of the extrudate a random distribution of particles exists, particularly when thick-walled extruded material is manufactured. Moreover it has been erroneously assumed heretofore that for an increase of the stiffness of the extrudate material, a considerable compression of the mixture must be provided in the precompression process. The more intensive is the compression in the precompression process however, the less of a binding is experienced by the separately precompressed increments of the extrudate product pressed against one another in the extruder in the extrusion direction. Indeed tests have shown that products formed by this process art process can be comparatively easily broken along the binding surfaces of the individual parts or layers and no useful value with respect to the stiffness and strength is attained.